1. Field of the Invention
The present invention relates to a warning system, particularly to a warning system which is capable of detecting a thief who breaks a house window and intrudes into the house and which produces an alarm. This invention also relates to an alarm signal generation device forming the warning system.
2. Description of the Related Art
In order to deal with a theft in which a thief breaks a house window and then intrudes into the house, there have been suggested various types of warning systems. A typical example for a warning system is formed by attaching an impact sensor to a window or to a window frame, in a manner such that when the window is broken and an impact is thus caused to the window, the impact sensor will send out a signal which will be received by an alarm device so that the alarm device can produce a warning notice.
However, the above-described conventional warning system is so formed that its impact sensor will respond not only to an impact caused by a thief breaking the window, but also to a window vibration caused due to rain and/or wind, as well as to the vibration of the window caused due to noise close to the house. As a result, it is difficult to avoid an inconvenience in which a warning notice will be undesirably produced even when it is not necessary.
It is an object of the present invention to provide an improved warning system and an improved alarm signal output device, capable of distinguishing a real theft from a window vibration caused due to other reasons, thereby correctly detecting a theft and thus correctly producing a warning notice.
A warning system constructed according to the present invention comprises an electric signal output device capable of resonating with an ultrasonic wave having a frequency within a predetermined frequency band and thus outputting an electric signal; a signal detection device capable of detecting only a signal component having a specific frequency from the electric signal output from the electric signal output device; an alarm signal output device capable of outputting an alarm signal in accordance with the detection of the signal component having the specific frequency, said detection being carried out by the signal detection device; and a warning notice producing device capable of producing a waring notice in accordance with an alarm signal fed from the alarm signal output device.
The aforementioned warning system can be put into practical use by for example attaching the electric signal output device to a window, so that as soon as an invader breaks a window and thus an impact is caused to the window, the electric signal output device will resonate with an ultrasonic wave having a frequency within a predetermined specific frequency band and mixed with other ultrasonic waves caused due to the above impact, thereby producing an electric signal. In this way, only a signal component having a specific frequency can be detected from the electric signal, by means of the signal detection device. Therefore, the alarm signal output device can operate to output an alarm signal based on the detected signal component having a specific frequency. As a result, a warning notice can be produced by the warning notice producing device in accordance with the alarm signal.
Accordingly, with the use of the aforementioned warning system, it is possible to catch and distinguish an impact caused by an intruder to the window, from other sorts of impacts caused by other factors such as rain and/or wind, thereby generating an automatic and correct production of a warning notice at a time the window has been truly broken.
Here, as the electric signal output device, it is possible to use a piezo-electric element or a piezo-electric material. In particular, it is preferred that a piezo-electric ceramic be used. Further, as the signal detection device, it is possible to use a resonator such as an LC resonator. Moreover, as a warning notice to be produced by the warning notice producing device, it is possible to employ a warning notice which is in the form of sound or light.
In addition, in a preferred embodiment of the present invention, the warning system may be so formed that its signal detection device can operate to detect, as a single component having a specific frequency, an ultrasonic wave signal generated immediately before the breaking of a window. In this way, it is possible to correctly distinguish, from other sorts of signals, an ultrasonic wave signal which has a specific frequency and caused due to the breakage of the window.
In another preferred embodiment of the present invention, the warning system is so formed that it is possible to provide a semiconductor switch which receives an output of the signal detection device and then starts the alarm signal output device. In this way, it is possible to carry out a high precision On/Off control of the output of the alarm signal during a predetermined time period.
A warning system according to a further embodiment of the present invention comprises an electric signal output device capable of resonating with an ultrasonic wave having a frequency within a predetermined frequency band and thus outputting an electric signal; a signal detection device capable of detecting only a signal component having a specific frequency from the electric signal output from the electric signal output device; an alarm signal output device capable of outputting, for a predetermined time period, an alarm signal in accordance with the detection of the signal component having the specific frequency, said detection being carried out by the signal detection device; and a warning notice producing device capable of producing a warning notice in accordance with an alarm signal fed from the alarm signal output device.
Further, an alarm signal output device of the present invention comprises an electric signal output device capable of resonating with an ultrasonic wave having a frequency within a predetermined frequency band and thus outputting an electric signal; a signal detection device capable of detecting only a signal component having a specific frequency from the electric signal output from the electric signal output device; an alarm signal output device capable of outputting an alarm signal in accordance with the detection of the signal component having the specific frequency, said detection being carried out by the signal detection device.